This invention relates to the treatment of water, especially chilled water, previously used in a food processing environment so as to remove fat, protein, microorganisms and other impurities therefrom and to improve the light transmission properties of the water to allow a substantial amount of the water to be reused with only minimal additional cooling.
In the food processing industry, chilled water is used for the purpose of cooling the food product being processed, especially chicken carcasses and other meat products. Such cooling is usually by direct contact of the food product with the chilled water and, where the food product is not previously sealed in a container, a portion of the product becomes waterborne in an amount that, while small relative to the volume of water, contaminates the water and makes it cloudy or dark thereby making it unreusable for the same process. In some industries, substantial volumes of cooling water are required for each unit of food product processed. Traditionally, the water is obtained, cooled, used in the food process and discharged. This discharged wastewater usually contains large amounts of fat, protein, bacteria, solids and other impurities.
In the United States, the regulations regarding quantity and quality of chilled water for use in the poultry industry are promulgated by the U.S. Department of Agriculture. Many of these regulations are set forth in 9 CFR Ch. III Sec. 381.66. These regulations require certain quantities of chilled water to be used for each bird carcass (for example, one-half gallon of chilled water for each frying chicken and one gallon for each turkey). Further, the regulations impose certain quality requirements for recycled chiller water including reduction of microorganisms prior to reuse and minimum light transmission as a percentage of fresh make-up water. For various levels of quality, different quantities of recycled water must be used to replace each gallon of fresh water. For example, if microorganisms are reduced at least 98% in the recycled water and light transmission is at least 80% of that of the fresh water, then 1.10 gallons of recycled water must be used to replace each gallon of fresh water called for by the regulations.
Of all the costs involved in such a process, the most expensive step is cooling the water. Also, a large supply of fresh water may be difficult to obtain. Therefore, a method of processing water to allow the water to be recycled as cooling water in the food processing without a significant change in temperature is desirable and economical, even if somewhat more recycled water must be used as compared to fresh water.
There are a number of processes in existence for removing fats and other emulsified impurities from wastewater. Some of these processes have used some sort of air floatation (normally air bubbles injected near the bottom of the wastewater) to break emulsions in the wastewater so as to float the fat to the surface to allow removal of the fat from the water.
In other processes, the wastewater is treated with ozone to oxidize impurities in the water. For example, Sheldon in the Journal of Food Science, Vol. 51, No. 2, pages 305 to 309, 1986, discusses a process for disinfecting poultry chiller water using ozone. However, the Sheldon process does not provide for fat removal and the "air floatation" processes are inefficient and do not provide for disinfecting the water.
The present invention, however, provides an ozone and air treatment of wastewater in which the ozone not only oxidizes impurities (thereby killing microorganisms and generally disinfecting the water), but also aids in the fat removal process. In particular, applicant has found that a combined ozone and air mixture bubbled up through wastewater in a tower, with a suitable flow of the mixture and proper overflow design of the tower, provides for a better separation of fat from the water than does the conventional use of air bubbles alone. It is theorized that ozone alters the free surface energy relationship, of the mixture bubbles which allows or promotes adsorption of fats, oils, gases and other impurities on the surface of the ozone/air bubbles. The bubbles then carry the adsorbed material to the water surface and form a foam layer. By proper positioning of an overflow for the tower, the foam is diverted from the tower so that the fats are separated from the wastewater stream.
The present invention makes it possible to simply and efficiently simultaneously remove fat from the wastewater that would otherwise quickly block filter systems, while disinfecting the water and preparing the water for reuse in the food cooling process. The processed water constitutes a much lower refrigeration load for food processing than would be required for fresh water and the volume of makeup fresh water to the process is greatly reduced thereby reducing both fresh water and refrigeration costs.